Electric timer and sequencing system for pyrotechnic flash items



C. L. SMITH ELECTRIC TIMER AND SEQUENCING SYSTEM Filed June 28, 1961 FOR PYROTECHNIC FLASH ITEMS Aug. 6, 1963 INVENTOR. Chaseer L- Eimith J Qr ao a. JQ f 294mg United States Patent 3,099,962 ELECTRIC TIMER AND SEQUENCING SYSTEM FOR PYROTECHNIC FLASH ITEMS Chester L. Smith, Wharton, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed June 28, 1961, Ser. No. 120,447 3 Claims. (Cl. 102-702) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon.

The present invention relates to improvements in delay timers and the like and pertains more particularly to new and improved means for timing, sequencing and initiating pyrotechnic light sources utilized in missile tracking operations. Reliable tracking data, as obtained from photographic means, depends to a great extent on the accurate periodic sequencing of pyrotechnic light sources, and such data reveals, among other things, the extent to which the tracke'cl'ohject may be tumbling, spinning, or otherwise deviating from its intended performance.

In the field of delay timers, especially those used for missile tracking purposes, it has been the general practice to employ a plurality of conventional R-C type timer circuits serially connected Where a capacitor is charged in a logarithmic relation with time until the pyrotechnic device in that circuit has fired, at which time the sequence progresses to the next circuit. Each successive R-C constant in this type of prior art arrangement is greater than the previous, thereby providing the necessary sequencing characteristics. However, these prior art devices have not proved entirely satisfactory for all purposes and have the disadvantage of low reliability and also lack an accurate time interval between flashing sequences thereby affecting the reproducibility of timing. The present invention overcomes these disadvantages.

Accordingly, an object of this invention is to produce a circuit design and fuzing technique which will provide a time delay circuit capable of automatically sequencing and timing the firing of selected events.

Another object of this invention is to provide a reliable and simplified method of initiating events incorporating an inherently accurate and reproducible sequence of delay times.

A further object is to produce an electrical timing and sequencing circuit which requires a few components and occupies a minimum of space to perform its intended function.

These and other objects will hereinafter become more full apparent from the following description of the annexed drawing in which is illustrated a preferred embodiment depicting a circuit employing the principles of this invention.

Many features of this invention are due in part to the use of transistor type components.

Referring now with greater particularity to the drawing, there is shown a circuit for sequentially initiating a plurality of conventional pyrotechnic fiash items (not shown).

This circuit comprises an R-C timer circuit comprised of a power source 14, switch 18, resistor and capacitor 19 connected in parallel with a plurality of squib circuits. Each of the squib circuits is comprised of a diode and an explosive squib, for example diode 15 and explosive squib 11. Similarly, diode 16 with squib 12, and diode 17 with squib 13, respectively, iform the remaining squib circuits. interposed between the squib "ice circuits and the RC timer circuit is a silicon semi-conductor grid-controlled rectifier 23 serially connected to resistance 24 which functions to discharge capacitor 19 to a predetermined voltage level following the firing of each squib circuit. The rectifier 23 is activated by an R-C circuit, namely 21, 22 and 26, 25 and 28, 27, respectively connected to each squib circuit.

This circuit operates a follows: When power from source 14 is applied to the circuit through switch 18, capacitor 19 acts as an apparent short circuit. Current flows through resistor 20 and capacitor 19 charges. When the voltage drop across capacitor 519 provides suflicient bias, current flows through four-layer diode 15, since its threshold of conductance is lower than diode 16 or 17. Capacitor 19 then discharge through diode 15, which may be considered the equivalent of a thyratron tube.

When diode 15 conducts, a current flows through explosive squib 11. Since the internal resistance of squib 11 is very small, the voltage drop across it is also very small and accordingly, the voltage drop across capacitor 21 can be considered negligible.

However, when explosive squib 1-1 ruptures, conduction thereby interrupted causing a large potential drop to appear across capacitor 21. Thus, a current limited by resistance 22 begins to flow, charging capacitor 21. It is of course understood that the time it takes to change capacitor 21 to the circuit potential is determined by the values of capacitor 21 and resistance 22. The energy pulse appearing at capacitor 21 acts to initiate the conduction of silicon semiconductor grid-controlled rectifier 23. Rectifier 23, in conjunction with resistance 24, thereby lowers the residual charge on capacitor 19 to a predetermined level which is a function of the voltage source 14, and the ratio of resistance 26 to the sum of the resistance 24- plus the internal resistance of rectifier 23.

The charge now remaining on capacitor 19 must be low enough to cause the potential drop across the combination resistance 24 and rectifier 23 to cause the rectifier to stop conducting. The rectifier will now remain in a nonconductive state even though capacitor 19 again changes in order to repeat this cycle. Since the circuit containing squib 11 is now open, the changing voltage will actuate diode 16 (which has a conductance level higher than diode 15 but lower than diode 17), resistance 25, capacitor 26 and fire squib 12 in the same manner heretofore described.

When this cycle has completely functioned, capacitor 19 will again charge and actuate diode 1'7, squib 13 and associated R-C components 27 and 28, respectively.

Thus, it can be seen that this invention provides a firing circuit of few parts and a high order of reliability. Further, since a common R-C circuit is employed, in cases where extreme accuracy is required, the work and time involved in the selection of components is greatly reduced. It is of course understood that this invention provides a system that can incorporate any number of firing events and thus provide any total time duration desired and still retain a high degree of accuracy and reliability.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. An electronic timing and sequencing system for initiating pyrotechnic flash items comprising: a single resistance-capacitance circuit, a plurality of subcircuits connected in parallel with the resistance-capacitance circuit and in tandem with each other, each subcircuit including a semiconductor and an explosive squib, said semiconductor consisting of a (four-layer diode; and a discharge circuit in parallel with the resistance-capacitance circuit, said discharge circuit including a silicon semiconductor grid-controlled rectifier and separate resistance-capacitive means for each of said four-layer diodes whereby each of said four-layer diodes is separately connected to said grid-controlled rectifier.

2. In combination:

a. An R-C timer circuit comprising a power source,

switch, resistor and capacitor;

b. A plurality of squib circuits comprising a diode and squib, said squib circuits .being connected in parallel with said R-C timer circuit;

c. A capacitor discharge circuit comprising a resistor and a silicon semiconductor grid-controlled rectifier, said capacitor discharge circuit being connected in parallel with said R-C timer circuit and said squib circuits; and

d. A plurality of R-C circuits comprising a resistor and capacitor, each of said R-C circuits being connected between each of said squib circuits and said capacitor discharge circuit.

3. An electrical timing and sequencing circuit for initiating pyrotechnic light sources utilized in missile tracking operations comprising, a source of electric power having a return connection and having a power line therefrom; a plurality of series circuits connected in parallel across said powerline and said return connection, each of the series circuits comprising a serially connected diode element and a squib unit, each diode element of the series circuits having a diiferent conductive level; a charging circuit connected between said power line and said I turn connection, said charging circuit providing the voltage necessary to initiate current flow through said diode elements; a discharge circuit connected between said power line and said return connection, said discharge circuit being used to lower the charging circuit to a predetermined level, and a plurality of R-C circuits connected between said discharge circuit and said parallel connections to provide for the desired timing.

References Cited in the file of this patent UNITED STATES PATENTS Minkler Mar. 14, 1933 

2. IN COMBINATION: A. AN R-C TIMER CIRCUIT COMPRISING A POWER SOURCE, SWITCH, RESISTOR AND CAPACITOR; B. A PLURALITY OF SQUIB CIRCUITS COMPRISING A DIODE AND SQUIB, SAID SQUIB CIRCUITS BEING CONNECTED IN PARALLEL WITH SAID R-C TIMER CIRCUIT; C. A CAPACITOR DISCHARGE CIRCUIT COMPRISING A RESISTOR AND A SILICON SEMICONDUCTOR GRID-CONTROLLED RECTIFIER, SAID CAPACITOR DISCHARGE CIRCUIT BEING CONNECTED IN 